Experimental study on acoustic emission characteristics of high-temperature thermal damage in an oxygen-rich environment of long flame coal

In the process of underground coal gasification, the development and evolution of cracks are vital for efficient coal gasification. In this paper, long flame coal is taken as a test object and heated to different temperatures (100–500 °C) in an oxygen-rich environment. The failure process of coal samples was analysed and monitored based on acoustic emission (AE) technique. The results show that the heating process of coal samples can be divided into two stages—room temperature to 300 °C and 300–500 °C—where the AE counts, energy and mass loss are closely related. Inflection points of the b -value occur at the temperatures of 250 and 400 °C corresponding to the change of AE counts. The cracks on the surface of coal samples gradually vary in width with the increase in heating temperature in the range of 100–400 °C, and the crack width becomes narrow at 500 °C due to the sealing of pores by tar condensation.